"Investors are just getting a little bit nervous with the continuing argument between Trump and China," he said.
The Fonterra Shareholders' Fund fell 2 per cent to $3.97 on a volume of 433,000 units, almost twice its 90-day average of 214,000. The fund had climbed 26 per cent since unveiling a new strategy, putting its New Zealand assets squarely at the centre of its efforts to pursue value over volume.
"After a great run following their result, it has come under some profit-taking pressure today," Williamson said.
A2 Milk Co declined 1.8 per cent to $12.81 and Synlait Milk fell 1.5 per cent to $9.02.
Chorus fell 1.2 per cent to $5.04 in relatively light trading of 213,000 shares, compared to its 522,000 average. The network operator announced former NBN and Telstra executive JB Rousselot will take over as chief executive next month. The company also unveiled strong connection growth for the September quarter.
Williamson said the new CEO appeared to have pretty good credentials and the quarterly connections went relatively well. But the stock was caught up in the broader market weakness, he said.
New Zealand Refining led the market lower, down 2.9 per cent at $2.02 on a volume of 166,000 shares, less than its 207,000 average.
Fletcher Building was the most traded stock on a volume of 2.2 million shares, more than its 1.3 million average. It fell 1 per cent to $4.80.
Ryman Healthcare rose 0.5 per cent to $13 on an unusually large volume of 2 million shares, almost five times its 417,000 average.
Of other stocks trading on volumes of more than a million shares, Spark New Zealand fell 0.8 per cent to $4.615, Meridian Energy dropped 2.5 per cent to $5.215, Auckland International Airport declined 1.4 per cent to $8.95, Contact Energy rose 0.6 per cent to $9.03 and Air New Zealand was down 0.7 per cent at $2.835.
Skellerup Holdings posted the day's biggest gain, up 4.6 per cent at $2.30 on a volume of 163,000 shares, in line with its 171,000 average. The rubber goods manufacturer told shareholders at today's annual meeting that it was on track to achieve more earnings growth in the current financial year.
"They were pretty upbeat expectations on future earnings growth in the current year," Williamson said.
Restaurant Brands New Zealand rose 2.9 per cent to $11.88 and Gentrack Group was up 2 per cent at $5.15.
Arvida Group increased 0.7 per cent to $1.47 after it noted the confirmation of a new surgical hospital in Queenstown was planned on land next to its Queenstown Country Club village.